[PATCH] Add -B flag to diff-* brothers.

A new diffcore transformation, diffcore-break.c, is introduced.

When the -B flag is given, a patch that represents a complete
rewrite is broken into a deletion followed by a creation.  This
makes it easier to review such a complete rewrite patch.

The -B flag takes the same syntax as the -M and -C flags to
specify the minimum amount of non-source material the resulting
file needs to have to be considered a complete rewrite, and
defaults to 99% if not specified.

As the new test t4008-diff-break-rewrite.sh demonstrates, if a
file is a complete rewrite, it is broken into a delete/create
pair, which can further be subjected to the usual rename
detection if -M or -C is used.  For example, if file0 gets
completely rewritten to make it as if it were rather based on
file1 which itself disappeared, the following happens:

    The original change looks like this:

	file0     --> file0' (quite different from file0)
	file1     --> /dev/null

    After diffcore-break runs, it would become this:

	file0     --> /dev/null
	/dev/null --> file0'
	file1     --> /dev/null

    Then diffcore-rename matches them up:

	file1     --> file0'

The internal score values are finer grained now.  Earlier
maximum of 10000 has been raised to 60000; there is no user
visible changes but there is no reason to waste available bits.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/diff-cache.c b/diff-cache.c
index c09782671..7d067a8f4 100644
--- a/diff-cache.c
+++ b/diff-cache.c
@@ -9,6 +9,7 @@ static int diff_setup_opt = 0;
 static int diff_score_opt = 0;
 static const char *pickaxe = NULL;
 static int pickaxe_opts = 0;
+static int diff_break_opt = -1;
 
 /* A file entry went away or appeared */
 static void show_file(const char *prefix, struct cache_entry *ce, unsigned char *sha1, unsigned int mode)
@@ -188,6 +189,10 @@ int main(int argc, const char **argv)
 			diff_output_format = DIFF_FORMAT_PATCH;
 			continue;
 		}
+		if (!strncmp(arg, "-B", 2)) {
+			diff_break_opt = diff_scoreopt_parse(arg);
+			continue;
+		}
 		if (!strncmp(arg, "-M", 2)) {
 			detect_rename = DIFF_DETECT_RENAME;
 			diff_score_opt = diff_scoreopt_parse(arg);
@@ -240,9 +245,11 @@ int main(int argc, const char **argv)
 		die("unable to read tree object %s", tree_name);
 
 	ret = diff_cache(active_cache, active_nr);
-	diffcore_std(pathspec,
+
+	diffcore_std(pathspec ? : NULL,
 		     detect_rename, diff_score_opt,
-		     pickaxe, pickaxe_opts);
+		     pickaxe, pickaxe_opts,
+		     diff_break_opt);
 	diff_flush(diff_output_format, 1);
 	return ret;
 }